1. Field of the Invention
The present invention relates to a zoom lens barrel which is used, for example, in a lens shutter type camera.
2. Description of Related Art
In a known camera having a zoom lens in which a lens barrel is moved in an optical axis direction by a helicoid mechanism, a cylindrical member of a lens advancing mechanism, which is provided on a peripheral surface thereof with a helicoid, is provided with a key way formed on the peripheral surface on which the helicoid is formed to move the lens barrel.
In a conventional lens shutter type camera having a zoom lens which is provided with a cam ring that is connected to an inner peripheral surface of a stationary ring (i.e., cylindrical member) secured to a camera body through male and female helicoids (i.e., helicoid mechanism) when the cam ring is rotated and, the zooming operation is carried out, the stationary ring is provided with a linear movement guide groove (i.e., key way) which extends in the optical axis direction thereof. Movable lens assemblies are received in the cam ring to move in the optical axis direction in accordance with the rotation of the cam ring. A linearly movable guide plate which is provided with an engaging projection that is fitted in the linear movement guide groove of the cam ring ensures the linear movement of the movable lens assemblies in the optical axis direction while preventing the rotation thereof.
In the above-mentioned known arrangement in which the linear movement guide groove is formed on the stationary ring and extends in the optical axis direction, it is necessary to provide a light intercepting member which closes a gap between the stationary ring and the cam ring in front of the linear movement guide groove to thereby prevent light from reaching a film surface through the linear movement guide groove.
The light intercepting member is continuously brought into forcible contact with the outer peripheral surface of the movable cam ring. Consequently, a frictional force is produced in the lens advancing mechanism which resists movement of the lens assemblies. This increases the power consumption of the battery.
The primary object of the present invention is to provide a zoom lens barrel in which light interception is ensured without the need to provide a special light intercepting member. In other words, the present invention is directed to preventing extraneous light from entering the camera through the key way formed on the cylindrical member.
To achieve the object mentioned above, in a zoom lens barrel having a cylindrical member which is provided on the periphery thereof with a helicoid and a key way extending in the optical axis direction, according to the present invention, the key way is formed by partially cutting away a portion of a helicoid.
According to an aspect of the present invention, a zoom lens barrel is provided which comprises a pair of cylindrical members which are interconnected by respective helicoids and, a discontinuous linear guide groove which is formed by cutting away outer peripheral portions of the helicoid, thereby forming a plurality of key grooves, wherein the guide groove is extended in a direction parallel with an optical axis of the zoom lens barrel.
According to another aspect of the present invention, a zoom lens barrel is provided with a cylindrical member having a helicoid on the periphery thereof, and a key way which extends in an optical axis direction of the lens barrel, wherein the key way is formed on the helicoid.
According to yet another aspect of the present invention, a zoom lens barrel is provided which comprises a pair of cylindrical members which are engaged with respective helicoids, and are rotatable with respect to one another. One of the helicoids is a discontinuous helicoid having a plurality of key grooves which are aligned in the optical axis direction of the lens barrel. A discontinuous linear guide groove is formed by the plurality of key grooves. The guide groove is extended in a direction parallel to an optical axis of the zoom lens barrel. In the case that the female helicoid is formed as the discontinuous helicoid, it is preferable that the distance between the optical axis of the zoom lens and the bottoms of the key grooves is less than a radius of a dedendum circle of the female helicoid. In the case that the male helicoid is formed as the discontinuous helicoid, it is preferable that the distance between the optical axis of the zoom lens and the bottoms of the key grooves is greater than a radius of a dedendum circle of the male helicoid.
The present disclosure relates to subject matter contained in Japanese patent application No. 5-4257 (filed on 93/1/13) which is expressly incorporated herein by reference in its entirety.